Field of the Invention
This invention relates to the design of screens for digital projection technology. More specifically, it relates to the face optical part of the projection screens, which is a front part for the audience and forms a visible image therefor. This invention mainly refers to passive back-reflective direct projection screens and light-transmitting rear projection screens forming an image from light pulses of the projection light sources at the stage of their final preparation for organoleptic visual perception by end users of video information.
Description of the Related Art
A digital image projected onto the screen represents a mosaic grid of pixels illuminated by a sequence of light pixel pulses of the image light source. Each aggregate frame pixel light pulse, discrete by area and time, reproduces the averaged and then digitized brightness of the main components of chroma level (red, green and blue, or RGB). The time sequence of pixels at a given screen position changes stepwise the brightness of backlight pulses of each of the primary color components of each image pixel, at least at a frame rate, for the direct end organoleptic perception by the audience.
The existing designs of retro-reflective and light-transmitting screens of rolled, suspended and rigid subtypes have a number of disadvantages significantly limiting the functionality of their application. The main disadvantages of the existing screens and systems based thereon will include the following.
1. Ambient light by external light sources, which reduces the contrast of the perceived image which dramatically decreases the distinctiveness of gray scale shades and demands a significant increase in light flux from its source. Therefore, the existing screens require almost complete blackout of premises for the rendering of full photographic footage latitude, which is not always desirable and sometimes even impossible, since it not only limits the additional functional needs of the audience accompanying the demonstration (for example, at lessons, lectures, seminars, conferences, roundtables, etc.), but is also fundamentally unacceptable in some cases for basic security reasons when working with young children and elderly persons with disabilities.
2. The visibility of image flickering associated with a time discrete sequence of the projection of film frames and their components. Pulse technogenic image frames illumination results not only in a loss of a part of the light flux from the projector, but also dramatically increases the load on eyesight, since there are no real sources of images of such a pulsed reflection nature of natural daylight, especially at a significant pulse ratio, such as in the light valve division of stereo pair frames in a 3D projection, where even the duration of light pulses of individual image frames becomes less than the time intervals between these pulses.
With the advent of electronic digital projection, which practically superseded the analog technology from all spheres of its application, new disadvantages were added to the existing ones in the analog technology:                the above-mentioned artificially created geometric piecewise linear extrapolation of analog images by imparting a single relatively representative discrete-bit value to the color and brightness parameters within the boundaries of each digitized image pixel in each image frame was added to the time frame-accurate piecewise linear extrapolation;        the stationary maximum contrast inter-pixel grid of the illuminated pixel borders, which is actually a systematic hindrance of the perception of useful information, such as additional graphic pseudo-information, which was not in the originally registered events and which represents artificial sharp differences (transient processes) of information signal parameters important for perception in the same coordinates of space and periods of useful information flow, artificially and regularly divided by this receiving matrix grid into separate surrogate shares not correlating with the identification marks of the registered objects;        additional time sampling, pulse intensification and increased duty ratio of the receipt of color frame pixel lighting pulses, especially reinforced during the sequential transmission of color components in one-matrix projectors, even more reinforced in the projectors with slow reaction of the matrices (liquid crystal LCD principle and its modifications) compared to a micromirror DLP, and even more complicated at the projection of 3D images in a system with sequential transmission of stereo frames for viewing same in light valve glasses alternately opening the view for each eye in synchronization with the destination of each frame of each story-relevant synchronous stereo pairs of the projector images.        
These well-known disadvantages lead to an inadequate and uncomfortable viewing, to a dramatic increase in load and fatigue of visual organs and the whole organoleptic perception of the audience, to the lack of efficiency of the projection systems in the conditions of moderate lighting in most practical cases of multimedia applications in the actually existing demonstration premises of virtually universal purpose and life support: at lessons in schools and at seminars and lectures at universities, at conferences, in studio apartments, in cafes, bars and restaurants, at discos and ballrooms, in sport and fitness centers, in conference rooms with remote access to materials and interlocutors, in situational and dispatch control centers, in medical and judicial institutions, in imitating simulators and gaming systems, as well as in a vast variety of other similar multimedia applications.
Aside from that, the existing projectors with even standardized HD quality formats do not allow perceiving the images in a wide angle of a natural view, to which the whole evolution of motion picture industry was coming gradually and deliberately pursuing its goal of the maximum involvement of a viewer in the events of demonstrated stories through the creation of virtual <<presence effect>>. The consequence of these ambitions was the stepwise change of projection formats in the analog cinema projection from the classic width to height 4:3 screen ratio to the widescreen 16:9 and then to the wide-format 2.35:1 view and to an even more modern “I-MAX” format standing for “image maximum”, referring to the solid angle maximality of possible perception of the entire image by each viewer at each moment of its demonstration. This development of formats and the accompanying change in the hall configuration from the longitudinal projection onto the short end wall to the transverse projection onto the longest longitudinal wall of the hall pursued its goal of a radical expansion of the solid angle of the image perception by viewers up to optimal values corresponding to the boundaries of natural perception (from 70 to 120-140 degrees horizontally) with the appropriate integration of peripheral vision most responsible for the perception of information images, volume and relative movements of visual objects throughout the whole field for at least the single-point eyesight, which includes its peripheral areas as well (Measurement Protocols for Medium-Field Distance Perception in Large-Screen Immersive Displays. http://www.cse.msstate.edu/˜swan/publications/papers/2009_Klein-etal_Distance-Percep-Large-Screen_IEEE-VR.pdf). However, the modern technology of electronic projection, even of the high-definition formats (HD) developed and standardized in view of the psycho-physiological thresholds of body-angle acuity of human vision, is reasonably recommended by the manufacturers for comfortable viewing distances not less than twice the width of the screen, which provides the value of image perception angle only about 30 degrees in the horizontal plane.
A number of inventions, e.g. RU 2078362, RU 2102786, RU 2324211, WO1998/045753, WO2004/0131853, is dedicated to the battle with some of these disadvantages.
The patent RU 2078362 describes the material for projection screens containing layers of fluorescent particles and mirror lenses distributed over the screen area. This solution helps struggle with the pulse nature of projection exposure using the interpolation redistribution of the screen illumination during the intervals between pulses. However, the spectral specificity of the afterglow of the phosphors specified in this invention makes it impossible to use this screen and its luminescent materials for adequate demonstration of the footage, and that's why such screens are intended only for devices creating original, background, and special lighting effects.
In the patent RU 2102786, refractive optical fiber layers located in the matrix plane to enhance the viewing angle, including in the ambient illumination conditions, are used in the screen matrix; at the same time, the arrangement direction of fibers in a layer is proposed to be made mainly perpendicular to the arrangement of fibers in the next layer. This technical solution does not account for the pixel structure of modern digital image formats and pursues the only goal of reducing the impact of ambient illumination, without dealing with the issues of optical interpolation both in its geometric and time schemes.
The design in the patent RU 2324211 is closest to the present invention. The patent uses a layer of focusing lenses over a layer of apertures positioned along the optical axis of each of the focusing layer lenses. As explained by the authors, the efficiency of this device is due to the fact that the projector light impinging the screen at low angles is focused by the lenses substantially more than the light of external sources, and thus reaches the light reflecting layer through the aperture openings. Among disadvantages of this known solution is its high structural and technological complexity and, accordingly, high price, as well as the regularity of the raster structure, an increment of which is fundamentally impossible to make much smaller compared to the pixel size on the screen, since the reduction of the size of optical cells in this case down to the commensuration with the wave length of incident light in air will cause a change of the laws of particle-beam optics to a fundamentally different concept of wave optics. Additionally, the comparability of the sizes of optical cells with pixel sizes causes diffraction effects in the Fraunhofer zone: regular raster structure beating with geometric periodicity of the digitized signals from the projectors.
Moreover, the strategic disadvantage of the approach used in the design disclosed in the patent RU 2324211 is the idea of the authors about the provision of high resolution for digital video systems by increasing the playback clarity of artificially added technogenic features of digital images, such as computer graphics and animation, texts, charts and other video products of the computer display origin and handling, which have no direct relation to reality registered with the use of sampling by analogy with the “Procrustean bed” method known since ancient times, rather than by recreating the informative details of the reproduced images as identification marks of the visual images of real objects in the dynamics of its movements. These technogenic information objects of computer graphics initially form within the boundaries of rectangular pixel grids of the mosaic image structure at a uniform color-brightness filling within the boundaries of each pixel and with an additional pulse time fragmentation of frame and color image component parts. They are initially technogenic, have no natural originals and detailed inner pixel structure, and therefore they cannot require an interpolation recovery of any intermediate values of the parameters during playback as it is required by the compressed digital samples of the filming of real objects implemented with the forced limited angular and temporal resolution within the used digitization standard and the used playback technology, but nevertheless intended to adequately present to the organoleptic perception the original analog realities having a priori an indefinitely high angular and time resolution.
Optical anisotropic structural elements in the form of optical fibers were used to improve the quality of the images obtained from optical screens for direct projection under external illumination conditions, as indicated in the U.S. Pat. No. 7,116,873, U.S. Pat. No. 6,741,779, U.S. Pat. No. 6,535,674 and in the International application WO2008/0285125. However, these known devices were aimed only at increasing the image contrast under external illumination conditions. Fundamentally unrepairable defects of the specified structures are their high technical and technological complexity inevitably resulting in the rise in the cost of products. Moreover, the geometrical regularity (periodicity, determinacy) of the optical heterogeneity of the working surface of such video interfaces inevitably contributes to the manifestations of interference with another geometric periodicity—a pixel grid of the projector light flux brightness, thereby resulting in the appearance of additional geometric patterns in the form of alternating lines, blotchiness and “feathers” with various chrominance and brightness due to the effect of beating of two or more periodic processes. These interference patterns, as well as the artifacts of image digitization mentioned above, are basically absent in the initial information. Their occurrence is also caused just by the imperfection of the technical means used for registration, compression, storage, processing, transmission and playback of the images. The common disadvantage of all these known devices is the absence of full consideration of perceptual psycho-physiological characteristics of the perception subjects of typical visual images and individual identification marks, inherent in the images of real footage objects, by the visual organs.
The main objective of the interpolation recovery of intermediate signal values deliberately discarded in the digitization process at the expense of the forced saving of scarce technical resources is a recreation of perceptually significant identification marks of information signals, which is implemented only until the visibility limits of the imported technogenic elements of pixelated images have been reached. Data compression in digital-to-analog recording devices is carried out through extrapolation sampling of conditionally representative luminance values of primary colors, further used by the modern signal recording algorithms for uniform filling the entire area of each pixel in this frame time interval. Such an algorithm of the initial compression of an information flow is typical for all systems of signal registration, which essentially are all the known formats of analog-to-digital signal conversions and codecs (both lossless and with information losses), being the devices of further compression of information signals at the expense of the discarding of conditionally insignificant and a priori recoverable parts of these signals. Mostly used to restore the intermediate values of video signals lost during sampling in the intellectual systems of image improvement and other devices of sample decoding up to progressive scan and scaler devices is an intellectual computer software for signal pre-processing employing the following two abilities of eyesight:
1) interpolating averaging of per-frame and intra-frame pulse values of chrominance components and signal luminance;
2) aprioristic pre-expectation of movements anticipating the likely changes in the boundary positions of characteristic identification marks and features of an observed real object at its natural movements and turns with respect to its surroundings in view of perspective distortions of scale, color saturation and atmospheric haze.
However, computer interpolating restoration of signal detail is a very effective means of restoring its informational content, if only the projection equipment has a many-fold higher pixel and frame resolution than the one inherent in the material being played. The possibilities of a significant image quality enhancement at the expense of a many-fold increase in the number of pixels virtually exhausted its potential with the appearance and introduction of cameras, codecs, monitors and projectors with high-definition formats (HD). Additionally, the strategy itself for reducing the visibility of the image digital nature by reducing the size of their discrete elements solves the problems by means of technology intensification and pursues only an indirect goal, not paying enough attention to the ultimate goal of the restoration of the original analog nature of the filmed originals of the displayed objects.
The existing projection systems, consisting of a light flow source (projector) and a projection screen, did not pay due attention until recently to a possible reduction of the visibility of digital structure of the images of real recognition objects directly on the screen, including the dynamics of movements of these objects. This lack of attention to the optical interpolation was encouraged also by the lack of reliable detailed data on the criteria for pixel image structure visibility in cinema projection, which left the developers of projection and screen technology only with the criteria of static thresholds of perceptible image difference for eyesight in photography (Measurement Protocols for Medium-Field Distance Perception in Large-Screen Immersive Displays. http://www.cse.msstate.edu/˜swan/publications/papers/2009_Klein-etal_Distance-Percep-Large-Screen_IEEE-VR.pdf).
A similar problem of interpolation restoration of image brightness intermediate values in a geometric plan was studied in radiological medical devices—CT scanners, on the information completeness therefrom the health and lives of patients depend, see U.S. Pat. Nos. 4,680,709 and 5,058,011. However, these devices produce an interpolation and holographic restoration of initially unknown specific details of the patient's anatomical anomalies presented in the form of analog information between sequential discrete value readouts of stationary object image settings at the defined changes of angular direction of the probing beam, and do that only due to the special software, without assigning a tasks of interpolation restoration of the pre-expected intermediate signal values in real time of incoming converted signals describing the moving objects.